LOL bring that poxy starlet to the next NZHondas track day at Taupo and we'll see just how much you can't really expect from an NA car... :roll:
To be perfectly honest you're kinda wasting your time with the Spec-S, if you wanted performance you should have saved a bit more and started with the Spec-R. You will get a small gain from doing I/H/E but it still won't get you close to a stock Spec-R.
But to answer your question, doing a few basic bolt-on mods shouldn't have any effect on the lifespan of your motor. Keep it well serviced, don't give it death when its cold, etc and you should have a good run with it. If you're more of a circuit/cornering guy then forget about the motor and spend some money on some decent coil-overs, lighter rims with good tyres (yes folks, wheels are actually a performance mod if you don't buy big ugly heavy chromes!!), and perhaps some uprated sway bars and braces. That way if you do decide to upgrade to a Spec-R (or just drop an SR20DET in) then you'll still be reaping the benefits, unlike you would with mods to the motor.
Speaking from personal experience, I got far more enjowment out of doing handling upgrades to my civic than I did doing a B18C-R swap, blowing a heap of cash on a new motor and close ratio box made it a heap quicker, but not really that much more fun than the stock B16A...